Light emitting diodes and laser diodes are well known solid state electronic devices capable of generating light upon application of a sufficient voltage. Light emitting diodes and laser diodes may be generally referred to as light emitting devices (“LEDs”). Light emitting devices generally include a p-n junction formed in an epitaxial layer grown on a substrate such as sapphire, silicon, silicon carbide, gallium arsenide and the like. The wavelength distribution of the light generated by the LED generally depends on the material from which the p-n junction is fabricated and the structure of the thin epitaxial layers that make up the active region of the device.
Typically, an LED includes a substrate, an n-type epitaxial region formed on the substrate and a p-type epitaxial region formed on the n-type epitaxial region (or vice-versa). In order to facilitate the application of a voltage to the device, an anode ohmic contact is formed on a p-type region of the device (typically, an exposed p-type epitaxial layer) and a cathode ohmic contact is formed on an n-type region of the device (such as the substrate or an exposed n-type epitaxial layer).
In order to use an LED in a circuit, it is known to enclose an LED in a package to provide environmental and/or mechanical protection, color selection, focusing and the like. An LED package also includes means, such as electrical leads or traces, for electrically connecting the LED chip to an external circuit. In a typical package 10 illustrated in FIG. 1A, an LED 12 is mounted on a reflective cup 13 by means of a solder bond or conductive epoxy. One or more wirebonds connect the ohmic contacts of the LED 12 to leads 15A, 15B, which may be attached to or integral with the reflective cup 13. The reflective cup may be filled with an encapsulant material 16 containing a wavelength conversion material such as a phosphor. Light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength. The entire assembly is then encapsulated in a clear protective resin 14, which may be molded in the shape of a lens to collimate the light emitted from the LED chip 12. While the reflective cup may direct light in an upward direction, optical losses may occur when the light is reflected (i.e. some light may be absorbed by the reflector cup instead of being reflected).
In another conventional package 20 illustrated in FIG. 1B, a plurality of LED chips 22 are mounted onto a printed circuit board (PCB) carrier 23. One or more wirebond connections are made between ohmic contacts on the LEDs 22 and electrical traces 25A, 25B on the PCB 23. Each mounted LED 22 is then covered with a drop of clear resin 24, which may provide environmental and mechanical protection to the chips while also acting as a lens. The individual packaged LEDs 22 may then be separated by sawing the PCB carrier 23 into small squares, each of which contains one or more LED chips 22.